Perl/Perlfaq

perlfaq

1. perlfaq1: General Questions About Perl

2. perlfaq2: Obtaining and Learning about Perl

3. perlfaq3: Programming Tools

4. perlfaq4: Data Manipulation

5. perlfaq5: Files and Formats

6. perlfaq6: Regular Expressions

7. perlfaq7: General Perl Language Issues

8. perlfaq8: System Interaction

9. perlfaq9: Networking

1. perlfaq1: General Questions About Perl

• [What is Perl?]
• [Who supports Perl? Who develops it? Why is it free?]
• [Which version of Perl should I use?]
• [What are Perl 4, Perl 5, or Perl 6?]
• [What was Ponie?]
• [What is Perl 6?]
• [How stable is Perl?]
• [Is Perl difficult to learn?]
• [How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?]
• [Can I do [task] in Perl?]
• [When shouldn't I program in Perl?]
• [What's the difference between "perl" and "Perl"?]
• [Is it a Perl program or a Perl script?]
• [What is a JAPH?]
• [Where can I get a list of Larry Wall witticisms?]
• [How can I convince others to use Perl?]

2. perlfaq2: Obtaining and Learning about Perl

• [What machines support perl? Where do I get it?]
• [How can I get a binary version of perl?]
• [I don't have a C compiler. How can I build my own Perl interpreter?]
• [I copied the perl binary from one machine to another, but scripts don't work.]
• [I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?]
• [What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?]
• [Is there an ISO or ANSI certified version of Perl?]
• [Where can I get information on Perl?]
• [What are the Perl newsgroups on Usenet? Where do I post questions?]
• [Where should I post source code?]
• [Perl Books]
• [Which magazines have Perl content?]
• [What mailing lists are there for Perl?]
• [Where are the archives for comp.lang.perl.misc?]
• [Where can I buy a commercial version of perl?]
• [Where do I send bug reports?]
• [What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org?]

3. perlfaq3: Programming Tools

• [How do I do (anything)?]
• [How can I use Perl interactively?]
• [Is there a Perl shell?]
• [How do I find which modules are installed on my system?]
• [How do I debug my Perl programs?]
• [How do I profile my Perl programs?]
• [How do I cross-reference my Perl programs?]
• [Is there a pretty-printer (formatter) for Perl?]
• [Is there a ctags for Perl?]
• [Is there an IDE or Windows Perl Editor?]
• [Where can I get Perl macros for vi?]
• [Where can I get perl-mode for emacs?]
• [How can I use curses with Perl?]
• [How can I write a GUI (X, Tk, Gtk, etc.) in Perl?]
• [How can I make my Perl program run faster?]
• [How can I make my Perl program take less memory?] - 메모리 사용량을 줄이는 방법 번역
• [Is it safe to return a reference to local or lexical data?]
• [How can I free an array or hash so my program shrinks?]
• [How can I make my CGI script more efficient?]
• [How can I hide the source for my Perl program?]
• [How can I compile my Perl program into byte code or C?]
• [How can I get #!perl to work on (MS-DOS,NT,...)?] - 윈도우에서 간편하게 실행시키기 번역
• [Can I write useful Perl programs on the command line?]
• [Why don't Perl one-liners work on my DOS/Mac/VMS system?]
• [Where can I learn about CGI or Web programming in Perl?]
• [Where can I learn about object-oriented Perl programming?]
• [Where can I learn about linking C with Perl?]
• [I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?]
• [When I tried to run my script, I got this message. What does it mean?]

4. perlfaq4: Data Manipulation

• [Data: Numbers]
  • [Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?]
  • [Why is int() broken?]
  • [Why isn't my octal data interpreted correctly?]
  • [Does Perl have a round() function? What about ceil() and floor()? Trig functions?]
  • [How do I convert between numeric representations/bases/radixes?]
  • [Why doesn't & work the way I want it to?]
  • [How do I multiply matrices?]
  • [How do I perform an operation on a series of integers?] - 연속된 정수에 연산을 수행할 때 - 번역
  • [How can I output Roman numerals?]
  • [Why aren't my random numbers random?]
  • [How do I get a random number between X and Y?]

• [Data: Dates]
  • [How do I find the day or week of the year?]
  • [How do I find the current century or millennium?]
  • [How can I compare two dates and find the difference?]
  • [How can I take a string and turn it into epoch seconds?]
  • [How can I find the Julian Day?]
  • [How do I find yesterday's date?]
  • [Does Perl have a Year 2000 problem? Is Perl Y2K compliant?]

• [Data: Strings]
  • [How do I validate input?]
  • [How do I unescape a string?]
  • [How do I remove consecutive pairs of characters?]
  • [How do I expand function calls in a string?]
  • [How do I find matching/nesting anything?]
  • [How do I reverse a string?]
  • [How do I expand tabs in a string?]
  • [How do I reformat a paragraph?]
  • [How can I access or change N characters of a string?]
  • [How do I change the Nth occurrence of something?]
  • [How can I count the number of occurrences of a substring within a string?]
  • [How do I capitalize all the words on one line?]
  • [How can I split a [character] delimited string except when inside [character]?]
  • [How do I strip blank space from the beginning/end of a string?]
  • [How do I pad a string with blanks or pad a number with zeroes?]
  • [How do I extract selected columns from a string?]
  • [How do I find the soundex value of a string?]
  • [How can I expand variables in text strings?]
  • [What's wrong with always quoting "$vars"?]
  • [Why don't my <<HERE documents work?]

• [Data: Arrays]
  • [What is the difference between a list and an array?] 리스트와 배열의 관계 - 번역
  • [What is the difference between $array[1] and @array[1]?]
  • [How can I remove duplicate elements from a list or array?] - 중복된 원소 삭제 - 번역
  • [How can I tell whether a certain element is contained in a list or array?]
  • [How do I compute the difference of two arrays? How do I compute the intersection of two arrays?]
  • [How do I test whether two arrays or hashes are equal?]
  • [How do I find the first array element for which a condition is true?]
  • [How do I handle linked lists?]
  • [How do I handle circular lists?]
  • [How do I shuffle an array randomly?]
  • [How do I process/modify each element of an array?]
  • [How do I select a random element from an array?]
  • [How do I permute N elements of a list?]
  • [How do I sort an array by (anything)?]
  • [How do I manipulate arrays of bits?]
  • [Why does defined() return true on empty arrays and hashes?]

• [Data: Hashes (Associative Arrays)]
  • [How do I process an entire hash?]
  • [How do I merge two hashes?]
  • [What happens if I add or remove keys from a hash while iterating over it?]
  • [How do I look up a hash element by value?]
  • [How can I know how many entries are in a hash?]
  • [How do I sort a hash (optionally by value instead of key)?]
  • [How can I always keep my hash sorted?]
  • [What's the difference between "delete" and "undef" with hashes?]
  • [Why don't my tied hashes make the defined/exists distinction?]
  • [How do I reset an each() operation part-way through?]
  • [How can I get the unique keys from two hashes?] - 고유한 키 추출 - 번역
  • [How can I store a multidimensional array in a DBM file?]
  • [How can I make my hash remember the order I put elements into it?]
  • [Why does passing a subroutine an undefined element in a hash create it?]
  • [How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?]
  • [How can I use a reference as a hash key?]

• [Data: Misc]
  • [How do I handle binary data correctly?]
  • [How do I determine whether a scalar is a number/whole/integer/float?]
  • [How do I keep persistent data across program calls?]
  • [How do I print out or copy a recursive data structure?]
  • [How do I define methods for every class/object?]
  • [How do I verify a credit card checksum?]
  • [How do I pack arrays of doubles or floats for XS code?]

5. perlfaq5: Files and Formats

• [How do I flush/unbuffer an output filehandle? Why must I do this?]
• [How do I change, delete, or insert a line in a file, or append to the beginning of a file?]
• [How do I count the number of lines in a file?]
• [How can I use Perl's 1 option from within a program?]
• [How can I copy a file?]
• [How do I make a temporary file name?]
• [How can I manipulate fixed-record-length files?]
• [How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?]
• [How can I use a filehandle indirectly?]
• [How can I set up a footer format to be used with write()?]
• [How can I write() into a string?]
• [How can I open a filehandle to a string?]
• [How can I output my numbers with commas added?]
• [How can I translate tildes (~) in a filename?]
• [How come when I open a file read-write it wipes it out?]
• [Why do I sometimes get an "Argument list too long" when I use <*>?]
• [Is there a leak/bug in glob()?]
• [How can I open a file with a leading ">" or trailing blanks?]
• [How can I reliably rename a file?]
• [How can I lock a file?]
• [Why can't I just open(FH, ">file.lock")?]
• [I still don't get locking. I just want to increment the number in the file. How can I do this?]
• [All I want to do is append a small amount of text to the end of a file. Do I still have to use locking?]
• [How do I randomly update a binary file?]
• [How do I get a file's timestamp in perl?]
• [How do I set a file's timestamp in perl?]
• [How do I print to more than one file at once?]
• [How can I read in an entire file all at once?]
• [How can I read in a file by paragraphs?]
• [How can I read a single character from a file? From the keyboard?]
• [How can I tell whether there's a character waiting on a filehandle?]
• [How do I do a 2 in perl?]
• [How do I dup() a filehandle in Perl?]
• [How do I close a file descriptor by number?]
• [Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work?]
• [Why doesn't glob("*.*") get all the files?]
• [Why does Perl let me delete read-only files? Why does 3 clobber protected files? Isn't this a bug in Perl?]
• [How do I select a random line from a file?]
• [Why do I get weird spaces when I print an array of lines?]

6. perlfaq6: Regular Expressions

• [How can I hope to use regular expressions without creating illegible and unmaintainable code?]
• [I'm having trouble matching over more than one line. What's wrong?]
• [How can I pull out lines between two patterns that are themselves on different lines?]
• [How do I match XML, HTML, or other nasty, ugly things with a regex?]
• [I put a regular expression into $/ but it didn't work. What's wrong?]
• [How do I substitute case insensitively on the LHS while preserving case on the RHS?]
• [How can I make 4 match national character sets?]
• [How can I match a locale-smart version of 5?]
• [How can I quote a variable to use in a regex?]
• [What is 6 really for?]
• [How do I use a regular expression to strip C style comments from a file?]
• [Can I use Perl regular expressions to match balanced text?]
• [What does it mean that regexes are greedy? How can I get around it?]
• [How do I process each word on each line?]
• [How can I print out a word-frequency or line-frequency summary?]
• [How can I do approximate matching?]
• [How do I efficiently match many regular expressions at once?]
• [Why don't word-boundary searches with 7 work for me?]
• [Why does using $&, $`, or $' slow my program down?]
• [What good is 8 in a regular expression?]
• [Are Perl regexes DFAs or NFAs? Are they POSIX compliant?]
• [What's wrong with using grep in a void context?]
• [How can I match strings with multibyte characters?]
• [How do I match a regular expression that's in a variable?]

7. perlfaq7: General Perl Language Issues

• [Can I get a BNF/yacc/RE for the Perl language?]
• [What are all these $@%&* punctuation signs, and how do I know when to use them?]
• [Do I always/never have to quote my strings or use semicolons and commas?]
• [How do I skip some return values?]
• [How do I temporarily block warnings?]
• [What's an extension?]
• [Why do Perl operators have different precedence than C operators?]
• [How do I declare/create a structure?]
• [How do I create a module?]
• [How do I adopt or take over a module already on CPAN?]
• [How do I create a class?]
• [How can I tell if a variable is tainted?]
• [What's a closure?]
• [What is variable suicide and how can I prevent it?]
• [How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?]
• [How do I create a static variable?]
• [What's the difference between dynamic and lexical (static) scoping? Between local() and my()?]
• [How can I access a dynamic variable while a similarly named lexical is in scope?]
• [What's the difference between deep and shallow binding?]
• [Why doesn't "my($foo) = <FILE>;" work right?]
• [How do I redefine a builtin function, operator, or method?]
• [What's the difference between calling a function as &foo and foo()?]
• [How do I create a switch or case statement?]
• [How can I catch accesses to undefined variables, functions, or methods?]
• [Why can't a method included in this same file be found?]
• [How can I find out my current or calling package?]
• [How can I comment out a large block of perl code?]
• [How do I clear a package?]
• [How can I use a variable as a variable name?]
• [What does "bad interpreter" mean?]

8. perlfaq8: System Interaction

• [How do I find out which operating system I'm running under?]
• [How come exec() doesn't return?]
• [How do I do fancy stuff with the keyboard/screen/mouse?]
• [How do I print something out in color?]
• [How do I read just one key without waiting for a return key?]
• [How do I check whether input is ready on the keyboard?]
• [How do I clear the screen?]
• [How do I get the screen size?]
• [How do I ask the user for a password?]
• [How do I read and write the serial port?]
• [How do I decode encrypted password files?]
• [How do I start a process in the background?]
• [How do I trap control characters/signals?]
• [How do I modify the shadow password file on a Unix system?]
• [How do I set the time and date?]
• [How can I sleep() or alarm() for under a second?]
• [How can I measure time under a second?]
• [How can I do an atexit() or setjmp()/longjmp()? (Exception handling)]
• [Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?]
• [How can I call my system's unique C functions from Perl?]
• [Where do I get the include files to do ioctl() or syscall()?]
• [Why do setuid perl scripts complain about kernel problems?]
• [How can I open a pipe both to and from a command?]
• [Why can't I get the output of a command with system()?]
• [How can I capture STDERR from an external command?]
• [Why doesn't open() return an error when a pipe open fails?]
• [What's wrong with using backticks in a void context?]
• [How can I call backticks without shell processing?]
• [Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?]
• [How can I convert my shell script to perl?]
• [Can I use perl to run a telnet or ftp session?]
• [How can I write expect in Perl?]
• [Is there a way to hide perl's command line from programs such as "ps"?]
• [I {changed directory, modified my environment} in a perl script. How come the change disappeared when I exited the script? How do I get my changes to be visible?]
• [How do I close a process's filehandle without waiting for it to complete?]
• [How do I fork a daemon process?]
• [How do I find out if I'm running interactively or not?]
• [How do I timeout a slow event?]
• [How do I set CPU limits?]
• [How do I avoid zombies on a Unix system?]
• [How do I use an SQL database?]
• [How do I make a system() exit on control-C?]
• [How do I open a file without blocking?]
• [How do I tell the difference between errors from the shell and perl?]
• [How do I install a module from CPAN?]
• [What's the difference between require and use?]
• [How do I keep my own module/library directory?]
• [How do I add the directory my program lives in to the module/library search path?]
• [How do I add a directory to my include path (@INC) at runtime?]
• [What is socket.ph and where do I get it?]

9. perlfaq9: Networking

• [What is the correct form of response from a CGI script?]
• [My CGI script runs from the command line but not the browser. (500 Server Error)]
• [How can I get better error messages from a CGI program?]
• [How do I remove HTML from a string?]
• [How do I extract URLs?]
• [How do I download a file from the user's machine? How do I open a file on another machine?]
• [How do I make an HTML pop-up menu with Perl?]
• [How do I fetch an HTML file?]
• [How do I automate an HTML form submission?]
• [How do I decode or create those %-encodings on the web?]
• [How do I redirect to another page?]
• [How do I put a password on my web pages?]
• [How do I edit my .htpasswd and .htgroup files with Perl?]
• [How do I make sure users can't enter values into a form that cause my CGI script to do bad things?]
• [How do I parse a mail header?]
• [How do I decode a CGI form?]
• [How do I check a valid mail address?]
• [How do I decode a MIME/BASE64 string?]
• [How do I return the user's mail address?]
• [How do I send mail?]
• [How do I use MIME to make an attachment to a mail message?]
• [How do I read mail?]
• [How do I find out my hostname, domainname, or IP address?]
• [How do I fetch a news article or the active newsgroups?]
• [How do I fetch/put an FTP file?]
• [How can I do RPC in Perl?]